As known in the art of internal combustion engines, during a cold start of such engines, certain components heat up and may experience thermal expansion. Additionally, over the life of an engine, engine components may wear, and thus change size and shape. Engine poppet valves (engine valves) and the systems used to actuate them (valve trains) are exposed to significant temperature changes and potential wear, and accordingly, these systems must allow for thermal growth and other phenomena that may affect actuation of the engine valves. One technique to accommodate thermal expansion and the like has been to provide a gap or lash space between the engine valve (or a valve bridge that spans two or more engine valves) and the valve train and/or between components of the valve train, such as a rocker arm, cam, push tube, etc. As the components experience thermal expansion, the lash space is taken up providing, ideally, a continuous mechanical connection between the engine valve and corresponding valve train or within the valve train itself. This lash space can be set manually, or in some cases, via an hydraulic lash adjuster between the engine valve and the valve train or within the valve train.
A hydraulic lash adjuster typically includes a sliding plunger within a housing and operated by a continuous supply of hydraulic fluid, such as engine oil. Unidirectional flow of hydraulic fluid into a chamber formed between the sliding plunger and the housing occurs when no actuations are applied to the engine valve, i.e., when the engine valve is closed and no or a relatively low load is placed on the lash adjuster. As the chamber fills with hydraulic fluid, the sliding plunger slides longitudinally within the housing thereby increasing the overall length of the hydraulic lash adjuster and taking up any lash within the valve train and engine valve linkage. On the other hand, when the engine valve is actuated (opened), i.e., a load is placed on the sliding plunger, a hydraulic lock within the chamber prevents the plunger from sliding.
Hydraulic lash adjustors, however, have not been used to adjust lash space between an engine valve and a valve actuation system designed to provide both positive power and auxiliary engine valve events (such as engine braking events) to the extent that such valve actuation systems typically include a so-called lost motion component. In the context of internal combustion engines, lost motion is a term applied to a class of technical solutions for modifying the valve motion dictated by a valve actuation motion source with a variable length mechanical, hydraulic or other linkage assembly. In a lost motion system the valve actuation motion source may provide the maximum dwell (time) and greatest lift motion needed over a full range of engine operating conditions. A variable length system may then be included in the valve train linkage between the valve to be opened and the valve actuation motion source to subtract or “lose” part or all of the motion imparted from the valve actuation motion source to the valve. This variable length system, or lost motion system may, when expanded fully, transmit all of the available motion to the valve and when contracted fully transmit none or a minimum amount of the available motion to the engine valve.
However, if an hydraulic lash adjuster is used in conjunction with a lost motion component, there is a risk that the hydraulic lash adjuster will function to take up available lash during periods of lost motion, thereby resulting in over-extension or “jacking out” of the hydraulic lash adjuster. In turn, this may result in the application of motions to engine valves that are supposed to be lost, thus creating the potential for catastrophic damage to the engine.
Thus, it would be advantageous to provide systems that address these shortcomings of existing systems.